International veterinary canine dyskinesia task force ECVN consensus statement: Terminology and classification

Abstract

Movement disorders are a heterogeneous group of clinical syndromes in humans and animals characterized by involuntary movements without changes in consciousness. Canine movement disorders broadly include tremors, peripheral nerve hyperexcitability disorders, paroxysmal dyskinesia, and dystonia. Of these, canine paroxysmal dyskinesias remain one of the more difficult to identify and characterize in dogs. Canine paroxysmal dyskinesias include an array of movement disorders in which there is a recurrent episode of abnormal, involuntary, movement. In this consensus statement, we recommend standard terminology for describing the various movement disorders with an emphasis on paroxysmal dyskinesia, as well as a preliminary classification and clinical approach to reporting cases. In the clinical approach to movement disorders, we recommend categorizing movements into hyperkinetic vs hypokinetic, paroxysmal vs persistent, exercise-induced vs not related to exercise, using a detailed description of movements using the recommended terminology presented here, differentiating movement disorders vs other differential diagnoses, and then finally, determining whether the paroxysmal dyskinesia is due to either inherited or acquired etiologies. This consensus statement represents a starting point for consistent reporting of clinical descriptions and terminology associated with canine movement disorders, with additional focus on paroxysmal dyskinesia. With consistent reporting and identification of additional genetic mutations responsible for these disorders, our understanding of the phenotype, genotype, and pathophysiology will continue to develop and inform further modification of these recommendations.

Keywords: dystonia; movement disorder; myoclonus; myokymia; myotonia; paroxysmal dyskinesia.

FIGURE 1

Thalamo‐cortico‐basal ganglia circuits involved in movement disorders. In the direct pathway of the basal nuclei (A), dopaminergic innervation of the caudate/putamen from the SNc increases inhibition of the SNr (and EPN not shown) by activating D₁R on GABAergic MSN. This releases the thalamus from tonic inhibition of these nuclei. Loss of this inhibition increases the excitatory feedback from the thalamus to the motor cortex and caudate/putamen, thus promoting movement. The indirect pathway (B) has the opposite effect. MSN inhibit GABAergic neurons in the GP. This releases the subthalamic nucleus from tonic inhibition, increasing excitation of the SNr/EPN, and in turn inhibition of the thalamus. Decreased thalamic excitation of the motor cortex and caudate/putamen inhibits movement. Dopamine inhibits MSN in the indirect pathway through the D₂R (C). Thus dopamine promotes movement by increasing activity of the direct pathway (A) and decreasing activity in the indirect pathway (C). D₁R, D₁ dopamine receptor; D₂R, D₂ dopamine receptor; EPN, endopeduncular nucleus; GP, globus pallidus; MSN, medium spiny neurons; SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata

FIGURE 2

Classification algorithm of tremor in veterinary medicine, adapted from the 2‐Axis approach developed by the International Task Force for tremor in humans. ¹² The column on the left lists all the components of the clinical description of tremor in patients. The flowchart extending to the right provides additional details to help describe those criteria on the left. In dogs and cats, idiopathic generalized tremor syndrome is classified as a kinetic tremor despite often being seen at rest